The present invention relates to a noise filter including a case and a tubular core assembled therein.
Hitherto, in noise filters, a magnetic core is disposed over an outer circumferential surface of an electric cable, thus absorbing noise current flowing through the electric cable. The core is brittle because it was made by baking or sintering. A case composed of two complementary halves is used for protecting the core and for mounting the core at a desired position of the electric cable.
In a conventional noise filter, a cable retaining segment is provided in the case. The cable retaining segment nips the electric cable. In this case, however, the case is inevitably complicated in shape. Consequently, a metal mold for molding the case is complex in shape. This lowers the productivity of the noise filter.
Laid-open Japanese Patent Application Publication No. 2004-193316 discloses a noise filter, in which a cable retaining segment is provided for respective halves of the case. The cable retaining segments nip the electric cable in the direction that is substantially perpendicular to parting faces of the complementary halves. Then, the electric cable contacts the cable retaining segments only at two points. In this case, an excessive pressure will be applied to the cable at one point if nipping force is to be increased. This may degrade durability of the electric cable.
To hold the electric cable by solely cable retaining segments in the opposite directions, sufficient rigidity is required in the cable retaining segments. In the latter case, however, such cable retaining segments do not provide sufficient nipping for an electric cable having relatively large diameter. Hence, the case with the rigid cable retaining segments is not available for holding various kinds of electric cables having various outer diameters.
A noise filter may be attached to an electric cable that is would once or a few times in a loop fashion, forming a bundle. If two cable retaining segments are used to hold the bundle of electric cable from the opposite directions, the electric cable, thus bundled, can hardly be held appropriately in its entirety.